Japanese Knotweed

What is Japanese knotweed?

Japanese knotweed (Fallopia japonica) is a bamboo-like perennial plant. Native to Japan, Taiwan and China, the plant was brought to the UK in 1825 for its attractive appearance. The plant was primarily popular with landscapers because of its ability to grow quickly and densely however it soon became known as a destructive species.

Japanese knotweed is now common across the UK with extensive infestations in the south-west of England, South Wales and Greater London.

Extracted from its harsher native habitat, Japanese knotweed grows rapidly and aggressively with the ability to grow up to 10cm a day. The root can grow to a depth of three metres. Its resilient stem is capable of suppressing all other plant growth and breaking through stone, brick, concrete and a variety of metals.

How can Japanese knotweed damage your property?

Japanese knotweed can cause damage to building structures by targeting the weak points such as cracks and attempting to grow through them. Knotweed can also damage tarmac and paving areas, building foundations, retaining wall structures and underground piping and drainage systems, which can drastically reduce the value of a property.

The BBC One Show featured a couple in Hertfordshire who lost £250,000 on their family home due to damage caused by Japanese knotweed.

Some mortgage lenders will decline mortgage applications due to the weed’s destructive nature or expect commitment to an effective treatment programme before considering an application.

Steps you should take

Most buildings insurance policies, including our Total Landlord Insurance do not cover damage and problems caused by Japanese knotweed, which is why a thorough surveyor’s report from a recognised governing body such as the Royal Institution of Chartered Surveyors is essential for identification of knotweed prior to purchasing a property.

Early detection of Japanese knotweed, is very important as the longer it is left, the more costly it becomes to remove. To give an example, it cost £70m to remove knotweed from the Olympic Park site before the 2012 Olympic Games.

The GB Non-Native Species Secretariat website provides identification sheets to help recognise species such as Japanese knotweed if you suspect an infestation. Alternatively, you can take photographs and e-mail them to a weed control company, who should be able to advise on whether or not the plant is Japanese knotweed.

Japanese knotweed is quite distinct, with tall purple speckled green bamboo like stems and heart-shaped leaves. Shoots have a red tinge and turn a lime green. In the summer months they produce cream flowers.

You don’t have to remove Japanese knotweed from your land, however it is included in the Wildlife and Countryside Act 1981, making it an offence to ‘plant or otherwise cause Japanese knotweed to grow in the wild’ or allowing it to spread onto anyone else’s property. Individuals could be fined up to £5,000 or be sent to prison for up to 2 years if contaminated soil or plant material from any waste you transfer spreads into the wild.

Once Japanese knotweed is established it can be challenging to remove. There are a number of options for effective treatment, such as excavation of the plant and its roots and biological or chemical control, the options recommended will vary depending on your particular circumstances. Choosing a PCA approved contractor to carry out the removal is recommended as these specialists have the ability to follow up the agreed work with a guarantee, meaning the risk of Japanese knotweed returning is minimised.

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